Acid-free closed-loop valorization of alkaline fly ash: Dual roles of H2O2 in peroxo-mediated ionic reshaping for selective Mo recovery and synergistic value enhancement of sodium carbonate

Similar geometries caused difficulty in (MoO 4 ) 2− and (CO 3 ) 2− separation. • A target-reshaping separation strategy based on CDFT descriptors was proposed. • Aliquat 336 selectively recovers 99.81% Mo as [Mo(O 2 ) 4 ] 2− without acidification. • Alkaline raffinate is directly converted to SPC achieving acid free valorization. Fly ash from petroleum refining waste alkali liquor incineration represents a dual-component secondary resource rich in sodium carbonate and molybdates. Conventional solvent extraction or ion-exchange resin for Mo recovery were usually applied in acidic aqueous environment, and selective separation of Mo from this highly alkaline (pH > 10) solution of fly ash was heavily hindered by similar ionic radii and charge densities of MoO 4 2− and CO 3 2− . Herein, we report an acid-free Mo extraction strategy based on peroxo complexation induced ionic reshaping. By introducing H 2 O 2 into fly ash solution, MoO 4 2− is quantitatively converted into the bulky [Mo(O 2 ) 4 ] 2− complex, expanding the molecular volume to 140.20 Å 3 and elevating ionic softness to 0.31 eV −1 . Approximately 99.81% of Mo in solution was selectively extracted using extractant Aliquat 336, and yielded H 2 MoO 4 product with the purity of 99.65%. Moreover, Aliquat 336 exhibits the highest softness among the tested extractants, which results in a stronger affinity for the softened peroxo-reshaped Mo species. Conceptual density functional theory (CDFT) calculations and hard-soft acid-base analysis reveal that these geometric and electronic alterations dramatically enhance Mo orbital compatibility and binding energy (−5.725 eV) with extractant Aliquat 336. Subsequently, Mo depleted raffinate was subjected into the production of sodium percarbonate, and around 83.68% of sodium carbonate was recycled as sodium percarbonate (SPC) with total metallic impurities below 0.02%. Overall, the introduction of H 2 O 2 contributes to selective Mo recovery and simultaneous value enhancement of Na 2 CO 3 , and this method provides a sustainable strategy for the valorization of complex hazardous wastes. Download: Download high-res image (143KB) Download: Download full-size image